The invention relates to an internal combustion engine, that is, to a reciprocating piston internal combustion engine with a variable compression ratio.
The publication F. G. Wirbeleit, K. Binder and D. Gwinner xe2x80x9cDevelopment of Piston with Variable Compression Height for increasing Efficiency and Specific Power Output of Combustion Enginesxe2x80x9d, SAE Tech. Pap., 900229 [1] discloses such a reciprocating piston internal combustion engine with a compression ratio, which is variable by changing the piston height. The piston of the internal combustion engine is comprised of two parts with hydraulic chambers disposed between them. The compression ratio is changed automatically by changing the position of one part of the piston with respect to the other part by the transfer of the fluid from one chamber to another.
The disadvantages of this known prototype include the fact that the system for varying the compression is disposed in a high temperature area (in the cylinder). Experience shows that the system described has a tendency, for example, to knock when changing the driving mode, for example during acceleration, as the control of the hydraulic system does not permit a rapid change of the compression ratio for all the cylinders at the same time.
The intention of removing the compression control mechanism from the high temperature area has led to another series of technical solutions, which provide a change in the kinematics of the internal combustion engine. These solutions include additional elements in the piston operating mechanism and means for influencing them so as to permit changing the compression ratio of the engine.
An internal combustion engine of a type [2] (FIG. 1), A. Jante xe2x80x9cKraftstoffsverbrauchsenkung von Verbrennungsmotoren durch kinematische Mittelxe2x80x9d, Automobilindustrie 1980, N1, pp. 61-65, is also known. This internal combustion engine includes two additional elements (additional connecting rod 13 and pivot lever 14) between the crank 15 and the connecting rod 12. The pivot lever 14 executes a pivoting movement starting from the articulation point Z. The compression ratio is varied on the basis of the basic position of the bearing point A being changed when the crank 15, which is attached to the casing of the internal combustions engine, is adjusted. The crank 15 rotates as a function of the engine load and in the process the articulation point Z moves on a circular path.
The publication [3] Christoph Bolling et al. xe2x80x9cKurbeltrieb fxc3xcr variable Verdichtungxe2x80x9d, MTZ 58 (1997) 11, pp 706-711 discloses an internal combustion engine of the type FEV (FIG. 2) which includes an additional connecting rod 13 between the crank 11 and the connecting rod 12. The connecting rod 12 is additionally connected to the pivot lever 14, which executes a pivoting movement starting from the articulation point Z. The compression ratio is varied on the basis of the basic position of this articulation point Z being changed when the crank 15, which is attached to the casing of the internal combustion engine, is adjusted. The crank 15 rotates as a function of the engine load, and in the process, the articulation point Z moves on a circular path.
The publication N DE4312954 A1 discloses an internal combustion engine of the type IFA [4] (FIG. 3) which includes an additional connecting rod 13 between the crank 11 and the connecting rod 12. The connecting rod 12 is additionally connected to one end of the pivot lever 14, the other end of which executes a pivoting movement starting from the articulation point Z. The compression ratio is varied on the basis of the basic position of the articulation point Z being changed when the crank 16, which is attached to the casing of the internal combustion engine, is adjusted. The crank 16 rotates as a function of the engine load, and in the process the articulation point Z moves on a circular path.
The disadvantages of the engines [2-4] described include primarily poor smoothness of running, which is due to the high second order oscillation forces of the masses which are moved in a translatory fashion by the kinematics of the operating mechanism. The arrangement furthermore requires an increase in the overall width or overall height of the assembly. This makes it impossible to use these internal combustion engines in the field of transportation.
A variable compression ratio in a reciprocating piston internal combustion engine however is advantageous because it can achieve the following objectives:
the average pressure Pe is increased as a result of an increase in the charge pressure without raising the maximum combustion pressure by reducing the compression ratio when the engine load increases;
the fuel consumption is reduced during low and medium load operation by increasing the compression when the engine load drops;
the operating smoothness of the engine is improved.
Depending on the type of internal combustion engine, the following advantages (for internal combustion engines operating according to the spark ignition principle) are obtained by virtue of the variable compression ratio:
While maintaining an economical operation of the engine which is achieved with low and medium loads, a further increase in the engine power is achieved by increasing the charge pressure while reducing the compression ratio (FIG. 4a).
While maintaining the nominal power level of the engine which is achieved with low and medium loads, the fuel consumption is improved by increasing the compression up to the permitted knocking level (FIG. 4b).
While maintaining the nominal power level of the engine, the economical operation with low and medium loads is improved and the noise level is reduced while the nominal rotational speed is simultaneously reduced (FIG. 4c).
For internal combustion engines operating according to the diesel principle, the variation of the compression can be developed in three equally prioritized directions:
Given a constant displacement and nominal rotational speed, the engine power is increased by the increase in the charge pressure. In this case, it is not the fuel consumption but rather the power output of the engine, which is improved (FIG. 5a).
Given a constant displacement and nominal power, the average pressure Pe is increased while the nominal rotational speed is lowered (FIG. 5b). In this case, while maintaining the power output of the vehicle, the economical operation of the engine is improved by increasing the mechanical efficiency (FIG. 5b).
An existing engine with a large displacement is replaced by an engine with a smaller displacement with the same power. In this case, the economical operation of the engine under medium and full loads is improved and the weight and the external dimensions of the engine are reduced.
It is the object of the invention to provide a reciprocating piston internal combustion engine, which includes a variable compression ratio that can be controlled with little structural expenditure, while the second order bearing forces and mass forces are reduced.
In a reciprocating piston internal combustion engine with a piston which is displaceably arranged in a cylinder and is coupled in an articulated fashion to a connecting rod whose movement can be transmitted to a crankshaft via a crank, a transmission element is provided between the connecting rod and a crank of the crankshaft and the movement of the transmission element can be manipulated by means of a control arm for an adjustment of the compression ratio of the engine.
In order to reduce second order forces, the transmission element is a transverse lever structure, which is coupled to the crankshaft via a joint, that is disposed in the intermediate region between a bearing connection of the transverse lever structure with the control arm and a bearing connection of the transverse lever with the connecting rod, the bearing connection of the transverse lever with the connecting rod, the crank and the control arm being arranged in a predetermined relationship.